Estimating range of VHF
I am in Europe and want to increase range of my VHF communication. I found formula for Radio Horizon that says
Horizon (km) = 3.569 * sqrt(height(meters))
How reliable is that formula in real environment (valley and forest) ? Does this mean that I just elevate my antenna and I get increase in range of VHF radio?
There is also 4/3 rule that says VHF will bend over horizon for 1/3 more then optical horizon. Does that mean my estimated distance of communication is 4/3 * formula above?
Quite true and reliable, except when certain propagation conditions permit, such as Tropospheric ducting (which is great, comes in real fast, not very common though).
Get your VHF antennas as high as possible, with the best coax you can find/afford because all that extra signal is lost on poor coaxial cable.
I think in practice the 4/3 rule is a bit conservative, you'll probably get a bit more than that, especially when beamed horizontally...
Do you have a formula that uses miles and feet? Meters make my American brain hurt in only away that Twinkies and crappy beer can fix.
KG7NDC
Horizon (miles) = 1.22 * sqrt(height(feet))
Any other suggestions how to improve range of VHF communication?
Since there is a lot of forest in the area of my interest, I have found following rule, on which I would like to hear opinions:
-----Rule for forest ------------------------
Antennas should be located in clearings on the edge farthest from the
distant station and as high as possible.
---------------------------
Your formula is good only for a flat plain ... no tress / foliage, no hills / mountains or major buildings the RF path as all of the objects can reduce the RF coverage. You must know what your Above Sea Level (ASL) or Ground Elevation is because that will contribute into the RF Distance covered. If you have a tower 14.28 m or 50' high and a high gain antenna +6 dB OMNI or +10 dB Yagi Beam, to add +6 dB automatically Double the height of the tower but you must keep your coaxial feedline losses near 1 dB or below using LMR-600 or 1/2" Heliax to experience the extra mileage out to the horizon. If you are operating Analog FM or Digital modes, make sure that the beam antenna is vertically polarized. If you are operating CW / SSB weak signal modes make sure that the beam is horiztally polarized, there is a minimum of 20 dB and as high as 30 dB losses in cross polarization contacts on the VHF & UHF Bands. If you decide to try Circular Polarization (mostly used for Satellite Opearation), there is a pro and a con for terrestrial over the horizon contacts. You will automatically lose 3 dB or 50% of your signal coverage which will reduce your line of sight by 25% and whatever that range is for your signal ... a station just beyond that will not hear your signal. On the other hand Circular Prevents the Doppler Effect or Mobile Flutter similar to Hill Topping / Picket Fencing, your signal is In & Out ... that doesn't exist with Circular.
Since we have no idea where you are located in Europe, it's very difficult to judge what type of Trees / Foliage you have so I'll provide some standard numbers for Regular Trees -3 dB or 50%, Dense Pine Trees -5 dB 0r 31.6% Signal Losses, for 50 foot Hills -11 dB or 14%, 100 foot Hills -13 dB or 20% Signal Losses and for Buildings in your Signal Path, Residential -2 dB 0r 60% and Commercial Buildings -10 dB or 10% Signal Losses. I realize that are other people with different opinions on Path Losses at VHF & UHF. Mine are based on System Engineering Data. For the most part if you were operating HF Bands the Path Losses would be very minimal because HF uses Sky Wave / the Atmosphere to bounce RF signals off of even if you were located very near Hills / Mountain range, any Trees / Foliage or Buildings.
You'll probably find that the best way to answer this question is to set up what you have and see. Avoid the obvious (e.g. keep the antenna above the trees). There are so many OBTWs ("Oh, by the way ... ) to anything like this that the best we can do is guess and look up formulae that may or may not take YOUR specific situation into account. Experiment! If Marconi hadn't been an experimenter we'd still be sending Transatlantic cables!
73
Pat K7KBN
Semper ubi sub ubi.
Hi WA9WVX,
Thank you for your post. I am wondering is there some kind of reference material where I can read more about those dB numbers for estimating Path Losses at VHF & UHF ? Preferably in .pdf form.
It occurs to me that adding up and down dB to copensate for antennas and forest is a lot like counting cards in poker.
KG7NDC
Glad you inquired as there are many PDF documents and other documents on the internet to enable you to learn:Originally Posted by Marko55
http://www.google.com/url?sa=t&rct=j...85076809,d.aWw
http://www.google.com/url?sa=t&rct=j...HycmXOu5tqaNlw
http://www.google.com/url?sa=t&rct=j...Zb2j3pYzC4nPxg
Here's a website that has many software packages for RF Coverage Mapping out the Terrain:
http://www.dxzone.com/catalog/Softwa...erage_Mapping/
How far can I talk based on an ARRL Ed Tilton:
http://www.k4lrg.org/Training/Tech_N...s/2M_Talk.html
Since you are in Europe I will recommend the RSGB Handbook or equivalent as a reference guide.
GT,
I've never played Poker but I suppose you're about right with those 52 cards a.k.a. dB Losses. ;-)
Dan
Hi WA9WVX,
Thank you for links you posted. I have seen some of that material, tho. But, I was interested where you get those estimates for losses for different kinds of forests or buildings. I understand, of course, that is just an rough estimate, but I would like to see some material giving those numbers, some source I can quote if needed.
Where I got that information was at Motorola International Systems Engineering and unfortunately that department no longer exist ... we had just about anything and everything including IBM computers with special software loaded into them do perform HF Studies, special handheld RF range calculators, topographical maps, all of the electrical specifications on every commercial two-way radio that was currently manufactured, Base Stations, Mobiles and Handhelds and Andrews Heliax Cables. I seriously doubt that you'll be able to acquire any of Motorola's or RF Harris in house technical propagation software for determining the VHF & UHF System Coverage Area.
In lieu of that information I have located another website that pertains to Amateur Radio VHF & UHF Coverage, and you better be good at Math, Calculus as there are quite a few formulas to accomplish the Path Losses for coverage. This is a PDF document so download it to your computer and start reading and working through the formulas.
http://www.google.com/url?sa=t&rct=j...DbqkAHSWXKwTUQ
Dan
WA9WVX
Don't forget to take into account "green leaf attenuation" and "RF sponges"... In my area we are surrounded by fairly thick pine tree forest. This is why even the repeater 25 miles northeast of me, with 100ft tower, and putting out 100W still only comes into my radio at S2-3 (and they get similar signal reception numbers on their side from my FT2900R using 75W). Soft wood trees and leaves, especially over distances can seriously degrade the signal. Then hard wood trees tend to bounce some of the signal causing some unusual multi-path propagation or signal loss due to it bouncing off in other directions.
So in valleys and thick forest, your better bet is get the antenna that much higher, either close to the top of a tree, or at the top of the hill.
Last edited by screwballl; Sat 14th Feb 2015 at 23:39.
de K4ISR
KM4FMK.com
Hi WA9WVX
So I looked into that article. Math is not that difficult, tho I didn’t checked the calculations myself. My principal problem is that is not “authorative source”, but single guy that is giving that approach, and that can not be for example quoted really, neither one can be sure that is all correct. For example that Harris book you recommended does not give such formulas.
But, calculating refraction losses looks fancy to me, if it is rally doable.
I have a bit of problem with understanding Fresnal’s zones and practical application for VHF. Formula I found says 1st Frasnel’s zone radius is
radius[meters]=8.657 * sqrt( distance [km]/frequency[GHz])
Let’s say I am working on 50MHz. Then for distance of 10 km, radius of 1st Fresnel’s zone is 122 m. Recommended 60% of zone that “needs to be clear” is 73 meters. So, in practical situation, I will always have obstacle in narrow 1st Fresnel’s zone. Than what is purpose of calculating 1st Fresnel’s zone one can never make it clear?
I got it for UHF, you get radius like 8 meters and then you try to put antennas so that 60% zone is clear from trees etc. For VHF that is not possible
Don't forget the ground absorbtion/reflectivity for VHF/UHF
Mark.
Since you're over in Europe, I'm not fimilar with your Terrain = Hills / Mountains, the type of Trees = Foliage, any Buildings = Residential / Commercial, the type of Feedlines & Lenght = RG-8/U, RG-213/U, RG-8X, LMR-400F, LMR-600 or Andrews Heliax RF Cables you plan to use, how much RF Power Output, type of an Antenna, Vertical (with Gain measurement) or Horizontal Yagi Beam (with Gain measurement) and if you intend to use a Structure (Tower) to support the Antennas, how high in Metres will it be? You have indicated 50 MHz which is a VHF Band but so is 70 MHz & 144 MHz and then UHF 430 MHz for Europe. All of the different items that I have listed play into the overall coverage and I haven'y even touched upon band conditions such as Tropo Ducting, Meter Scatter, Auroras and E-Skip or even the mode of operation, AM / FM / SSB / Digital these are all different on how they work and an individual should know what they are going to use ... I'm not that good at guessing what you are going to use and they all have advantages and disadvantages. Did you know that operating on the 50 MHz band using SSB, 10 W PEP RF Output and a 5 element Yagi Beam mounted at 5 Metres high, it is possible to work bona fide DX contacts over 1,000 miles or more away "if" the Atmosphere has the right conditions although on a regular day with out Atmospheric conditions with the same set up, you would be lucky to contact some one 30 miles away.
Back in the 1970s and 1980s, I was very active on 50 MHz, working stations out on the eastcoast, down south in Florida, Teaxs, Port-au-Prince, Haiti, Mexico, Brazil, the Carribean, out west in Idaho, Washington, Nevada, Utah, Colorado, New Mexico, up in Alaska, Canada, out in Hawaii from my home in Elgin, IL. I started out with a 10 W SSB transceiver, built up a 500 W RF amplifier and eventually bought a used Henry Tempo 1.5 KW RF amplier. I first had my beam at 10 Metres (35 feet) and eventually raised it up to 14 Metres (45 feet) which provided fairly good Ground wave and DX operations all on SSB. At the same time I was active on 144.2 MHz SSB, built up a 40 element phased collinear array muonting it at 18.5 Metres (65 feet) fed with 7/8" Heliax cable, a homebrew 2 Port RF Power Divider, a 10 W transceiver, buffer RF amplifier and my Tempo 6N2 KW RF amplifier. I have forgotten what year there was a DXpedition out on St. Paul Island in Nova Scotia, Canada using all of the Amateur Radio bands. There was a big pile up of hams on 144.2 MHz, I monitored for 5 minutes and then called the operator out there and gave my call sign and unkeyed the transceiver. I had broken the pile up using only 10 W PEP Output, in fact my signal was so strong, the operator out there gave me a 5 x 9 +40 dB over signal report and he wondered what I was using? It was a bit embarrassing since I was only using the basic 10 W transceiver, my amplifiers were just sitting standby. The operator out there was using 150 W PEP Output to his Yagi antennas. I'm very glad I didn't have the KW active in the circuit as it would have been a waste of time. And all of my effort that I put into the 2 m phased collinear array, tower and feedline paid off. Antennas are at the top of the heap for an Amateur Radio Station. That contact was 1,000 miles away ... it sort of blows the theory of Line Of Sight.
About a year later I was returning a rental camping trailer ... a small pop up and I had my 2 m SSB mobile turned on and listening to 144.2 MHz when the band popped open. I heard WB5LUA in Dallas, Texas calling CQ, I went back to him, gave him a signal report, my name and that I was operating from my mobile near Aurora, IL ... oh man, was he surprised to work a mobile that far away on 2 m SSB (roughly 1,000 miles), then I handed the mic over to my XYL and she worked him too. One CQ netted two call signs for his logbook. You can work far distances on FM simplex but remember the antenna, the height and the best feedline are key conponents on the Base Station, then add a RF amplifier to your FM transceiver.
Well that's about the best I can do for you, get your station up and operating and see how far you can talk.
Dan
WA9WVX
Hey WA9WVX,
Thank you for your posts. I am learning from them... They make this forum one more nice place on internet.
Cheers...
Thanks for providing such useful information.Thanks for sharing with all of us.
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